1. Field of the Invention
This invention relates generally to the field of magnetic tape transport systems, and more particularly, to a read/write head positioning device.
2. Related Art
In the course of developing various systems for the storage of data, data processing systems have traditionally utilized magnetic tape as a data storage medium. Typically, the magnetic tape is contained in an appropriate cartridge to facilitate the handling of the magnetic tape while in use as well as to protect the tape while in storage. An example of such a magnetic tape which has found applications in both the audio recording and computer industries is the data cartridge form as defined by American National Standard Institute (ANSI) Standard X3.180-1990. This cartridge has a single supply reel of magnetic tape that has a tape leader block attached to the free end of the tape. The IBM Model 3480 tape drive ("IBM" is a registered trademark of International Business Machines Company) utilizes this cartridge. Due to the prevalence of the 3480 tape drive system in the computer and data processing industries, this magnetic tape cartridge has become known in the industry as the 3480-type cartridge.
In common tape drive systems the magnetic tape cartridge in which the magnetic media is enclosed is inserted into a tape transport system. The magnetic tape is then wound and rewound between a supply reel contained within the tape cartridge and a take-up or machine reel in the tape transport system. The tape is transported along a tape path which brings the tape into contact with, or adjacent to, a magnetic tape head located along the tape path. Magnetic tape heads used in present-day tape drive systems are multi-track tape heads having separate read and write elements associated with each data track on the magnetic tape. This enables multi-track magnetic tape heads to read and write several streams of data (one per track) simultaneously. The magnetic tape is typically guided past the read/write head by air bearings which provide an interface of forced air with the magnetic tape to lower friction forces between the tape and bearing surface.
Examples of magnetic tape drive systems which store 18 tracks of data on the half-inch magnetic tape housed in the 3480-type cartridge are the StorageTek 4480 tape drive system, available from Storage Technology Corporation, Louisville, Colo., U.S.A., and the IBM 3480 tape drive system, available from IBM Corporation, Armonk, N.Y., U.S.A. Examples of magnetic tape drives which will store 36 tracks of data on the same half-inch magnetic tape are the (not yet publicly available but soon to be released) StorageTek 4940 and 4490 tape drive systems, manufactured by Storage Technology Corporation; and the IBM 3490 tape drive system, manufactured by IBM Corporation.
Recently, there has been a great demand for increasing the data throughput of magnetic tape transport systems used in conjunction with high-speed digital computers. In order to utilize the high-speed capabilities of these computers, it is necessary to increase the amount of data stored on a magnetic tape and to increase the speed at which the data is written to or retrieved from the magnetic tape media.
Of particular relevance is the advance in magnetic tape head technology to increase the track density of the magnetic tapes. Track density is defined as the number of data tracks per unit width of magnetic tape. Two characteristics associated with track density are track width, defined as the actual width of an individual data track; and track pitch, defined as the distance from the center of one data track to the center of a neighboring data track. As magnetic tape head size decreases, the track pitch and track width of a magnetic tape is decreased, thereby increasing track density.
Recently, improvements in the ability of magnetic tapes to store data at higher track densities has exceeded advances in magnetic tape head design. To continue to improve the data throughput of tape drive systems, these incongruous advances have lead to a need to read and write data to high density magnetic tapes, such as a 72 or 144 track half-inch magnetic tape, with a magnetic tape head having a lesser number of read/write elements.
One approach is to move the magnetic tape vertically while maintaining the magnetic head in a stationary position. However, attempts at moving the magnetic tape have been found to cause unrecoverable pertebations in the tape which prevent accurate data transfer, as well as cause excessive wear and damage to the magnetic tape.
Another approach which has been considerably more successful has been to vertically displace the magnetic tape head relative to the magnetic tape while maintaining accurate control of the magnetic tape along the tape path. One conventional approach to moving the read/write head has been to mount the read/write head on a leadscrew and, typically using a servo system, adjust the position of the head relative to a passing magnetic tape. This approach is described in U.S. Pat. No. 5,179,486 to Kraemer et al.
However, this and other conventional approaches have been found to be unacceptable for achieving the title movements necessary to accurately read data from a magnetic tapes having the increased track density described above.
Another problem with conventional tape head positioning devices is the inability to accurately displace the magnetic tape head in one axis without simultaneously causing significant rotation of the head.
What is needed therefore, is a read/write tape head positioning device capable of positioning the head for accurately reading and writing data on a high-density, thin film magnetic tape at very high speeds.